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Sounds a little goofy to me. Usually you see the limits and roll outs wired series in low volt. It may have been Jimmy rigged. Sometimes these modine units,especially older used a gas valve that had thermostat built in with probe and the blower cycled on and off when call for heat without delay off for blower. So basically that switch is probably a limit switch for low volt but somebody tried wiring blower line voltage to it thinking it was auxiliary blower switch.

I had a modine of that vintage and could not get parts from suppliers. I do not know what the issue was but I found some greenhouse websites that had good pictures, schematics and numbers. I pulled the modine part numbers from the site, called my supplier and gave him those numbers and he found the parts. It was like his information did not go back far enough. Those old moodines are tough... I have not seen many cracked compared to other brands of similar vintage.

Ive seen the limits wired both ways. Either turning off the trans former or just the gas valve, if the limit shuts off the primary side their is usualy a jumper wire from the input of the fan switch to the limit. Shouldnt be to hard to follow the wires. Let us know when u figure it out.

Got back to unit today, and traced all wireing. Traced wireing from fan delay and found coil on delay h1 and h2 were wired one to tr on gas valve and the other to tr-th(coil) on gas valve. moved this over to th on gas valve and unit worked correctly. Unit was working properly in the sense that limit would open and start the fan and shut off gas as a safety but it never had proper power to fan relay coil to start fan, in this case 20 seconds after burner started. I was told this unit worked by co-worker when he did his heat inspections, but now I dont think that was the case. I guess I did not think outside the box when my assumption was that this unit was in good running order and that well it must be wired right if someone said it was working when they last touched it. When is the th-tr coil used on a gas valve when you have tr and th terminals to power your circuit through?